# Constraints on Settings {#constraints-on-settings}
The constraints on settings can be defined in the `profiles` section of the `user.xml` configuration file and prohibit users from changing some of the settings with the `SET` query.
The constraints are defined as the following:
``` xml
lower_boundary
upper_boundary
lower_boundary
upper_boundary
```
If the user tries to violate the constraints an exception is thrown and the setting isn’t changed.
There are supported three types of constraints: `min`, `max`, `readonly`. The `min` and `max` constraints specify upper and lower boundaries for a numeric setting and can be used in combination. The `readonly` constraint specifies that the user cannot change the corresponding setting at all.
**Example:** Let `users.xml` includes lines:
``` xml
10000000000
0
...
5000000000
20000000000
```
The following queries all throw exceptions:
``` sql
SET max_memory_usage=20000000001;
SET max_memory_usage=4999999999;
SET force_index_by_date=1;
```
``` text
Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be greater than 20000000000.
Code: 452, e.displayText() = DB::Exception: Setting max_memory_usage should not be less than 5000000000.
Code: 452, e.displayText() = DB::Exception: Setting force_index_by_date should not be changed.
```
**Note:** the `default` profile has special handling: all the constraints defined for the `default` profile become the default constraints, so they restrict all the users until they’re overridden explicitly for these users.
[Original article](https://clickhouse.tech/docs/en/operations/settings/constraints_on_settings/)